NEW YORK — Occupy Wall Street protesters clogged streets and tied up traffic around the U.S. on Thursday to mark two months since the movement’s birth and signal they aren’t ready to quit, despite the breakup of many of their encampments by police. Hundreds of people were arrested, most of them in New York.

The demonstrations — which took place in cities including Los Angeles, Las Vegas, Boston, Washington, D.C., Seattle and Portland, Ore. — were for the most part peaceful. Most arrests were for blocking streets, and traffic disruptions were brief.

Chanting “All day, all week, shut down Wall Street,” more than 1,000 protesters gathered near the New York Stock Exchange and sat down in several intersections. Helmeted police officers broke up some of the gatherings, and operations at the stock market were not disrupted.

As darkness fell, a coalition of unions and progressive groups joined Occupy demonstrators in staging rallies at landmark bridges in several U.S. cities to protest joblessness.

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In New York, several thousand people, led by banner-carrying members of the Service Employees International Union, jammed Manhattan’s Foley Square and then marched peacefully across the Brooklyn Bridge on a pedestrian promenade.

As they walked, a powerful light projected the slogan “We are the 99 percent” — a reference to the Americans who aren’t superrich — on the side of a nearby skyscraper. Police officers dressed in Windbreakers, rather than riot gear, arrested at least two dozen people who walked onto the bridges’ roadway but otherwise let the marchers pass without incident.

Several weeks ago, an attempt to march across the bridge drew the first significant international attention to the Occupy movement as more than 700 people were arrested.

Thursday’s protests came two days after police raided and demolished the encampment at lower Manhattan’s Zuccotti Park that had served as headquarters of the Occupy movement and as demonstrators and union allies tried to regain their momentum.

At least 300 people were arrested in New York. Some were bloodied during the arrests. One man was taken into custody for throwing liquid, possibly vinegar, into the faces of several police officers, authorities said. Many demonstrators were carrying vinegar as an antidote for pepper spray. A police officer, Matthew Walters, needed 20 stitches on his hand after he was hit with a piece of thrown glass, police said.

In Los Angeles, about 500 sympathizers marched downtown between the Bank of America tower and Wells Fargo Plaza, chanting, “Banks got bailed out, we got sold out!” More than two dozen people were arrested.

Police arrested 21 demonstrators in Las Vegas, and 20 were led away in plastic handcuffs in Portland, Ore., for sitting on a bridge. At least a dozen were arrested in St. Louis after they sat down and locked arms in an attempt to block a bridge over the Mississippi River. More were handcuffed for blocking bridges in Philadelphia and Minneapolis.

In Chicago, hundreds of protesters organized by labor and community groups marched toward the Chicago River. They stopped at the river bridge and shut it down to rush-hour traffic. Police officers scrambled to divert cars and pedestrians.

New York Mayor Michael Bloomberg, meanwhile, said there had been “minimal disruption,” adding: “Most protesters have, in all fairness, acted responsibly.”